Effects of compliance boundary location on contaminant detection networks in aquifers

Groundwater monitoring networks were derived for 15 alternative compliance boundaries, located from 10 to 150 meters downgradient of a landfill. For each compliance boundary, a mass transport model was used to define the linear monitoring transect, perpendicular to groundwater flow, requiring the fewest detection wells. The distance (dt) to the optimal monitoring transect was consistently 0.40 to 0.75 times the distance to the compliance boundary (dc). Compliance boundaries located near a landfill provide capability for early detection, but also require a substantial number of closely spaced wells. As dc increases, the minimum number of wells (No) required along the optimal transect decreases. However, the rate of decrease (No/dc) is progressively smaller in the downgradient direction. And there is a value for dc, in this example 70 meters, beyond which the decrease in No is negligible.